Security system and warning method using edge detection of image signal

ABSTRACT

Disclosed are a warning generation method and a security system using edge detection of a video image signal. The warning generation method includes the steps of: a) decoding video image signals and extracting luminance signals from the decoded video image signals: b) filtering high-frequency components of the extracted luminance signals and detecting edge components within the video image signals: c) extracting only values within a range of a predetermined first threshold value form the detected edge componenets: d) accumulating the detected edge components for one video image: and e) operating a warning device if an accumulation value is smaller than a predetermined second threshold value. When an intruder blinds a camera lens using a cover, the security system can generate a warning by identifying the fact that the camera is blinded by the cover.

TECHNICAL FIELD

The present invention relates to a security system using video imagesignal capture, and more particularly to a warning generation method anda security system using edge detection of a video image signal, themethod and system being capable of informing a surveillant ofinformation indicating that a captured video image signal isinappropriate.

BACKGROUND ART

With the development of electric, electronic, computer and communicationtechniques, multimedia techniques for combining various informationpieces such as video information, audio information, etc. are newly andrapidly developed. A DVR (Digital Video Recorder) has been developed bythe advanced techniques described above. The DVR is employed in place ofan existing security system, i.e., a CCTV (Closed Circuit Television)system for security and surveillance. The CCTV records and stores avideo image for security and surveillance using an analog-typevideotape, etc., while the DVR digitalizes the video image and storesthe digitalized video image. The use of the DVR being a digital storagemedium is increasing because the DVR can generally improve quality of animage based on the continuous recording and storing of the existinganalog type.

Conventionally, a security system with a video capturing device and arecording device is used for monitoring a predetermined area orfollowing a criminal in an apartment complex, store, bank or etc.Security systems are widely used, but various methods are used to blockoperations of the security systems. For example, one method for blockingan operation of the security system is to cut an output line of a videocamera. Where the output line of the video camera is cut, there is aproblem in that the criminal cannot be appropriately identified throughthe surveillance for the predetermined area, because an appropriatevideo image is not displayed on or recorded in a display or recorder.

As techniques for addressing the above-described problem, there is amethod for generating a warning using a synchronous signal when aninappropriate video image signal is inputted.

FIG. 1 illustrates an exemplary configuration of a system for carryingout a warning generation procedure adopted in a conventional securitysystem.

In the conventional security system shown in FIG. 1, if video decoders10, 12 and 14 receive composite video signals outputted from videocameras, and detect synchronous signals to output the detectedsynchronous signals, a controller 16 controls driving of a warninggenerator by determining whether horizontal synchronous signals aredetected. Accordingly, because the horizontal synchronous signals cannotbe detected where the criminal cuts output lines of the video cameras, awarning sound is outputted at predetermined periods, and a surveillantcan perform an emergency action in response to the warning sound.

However, because an appropriate composite video signal is inputted whenthe criminal blinds a lens of a video camera by coating a foreignmaterial or using a cover, the controller 16 cannot generate a warningsound. In this case, assuming that the surveillant does not perform thesurveillance, the security system cannot be appropriately operated.

DISCLOSURE OF THE INVENTION

Therefore, the present invention has been made in view of the aboveproblem, and it is an object of the present invention to provide awarning generation method and a security system using edge detection ofa video image signal, the method and system being capable of sensing ablind state and informing a surveillant of an emergency situation when avideo camera is blinded by covering a camera lens.

In accordance with one aspect of the present invention, the above andother objects can be accomplished by the provision of a method forgenerating a warning using edge detection in a security system forreceiving video image signals outputted from a plurality of videocameras, and displaying or recording the video signals, comprising thesteps of: a) decoding video image signals and extracting luminancesignals from the decoded video image signals;

-   -   b) filtering high-frequency components of the extracted        luminance signals and detecting edge components within the video        image signals; c) extracting only values within a range of a        predetermined first threshold value from the detected edge        components; d) accumulating the detected edge components for one        video image; and e) operating a warning device if an        accumulation value is smaller than a predetermined second        threshold value.

In accordance with another aspect of the present invention, there isprovided a security system, comprising: a plurality of video cameras forproviding video image signals captured from surveillance areas; aplurality of video decoder for decoding video image signals from thevideo cameras and extracting luminance signals from the video imagesignals; and a blind detector for filtering a high-frequency componentof the luminance signal extracted from a corresponding video decoder,detecting edge components from the video image signals, extracting onlyvalues within a range of a predetermined first threshold value,accumulating the extracted values for one video image, and generating awarning signal if an accumulation value is smaller than a predeterminedsecond threshold value.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a view illustrating an exemplary configuration of a system forcarrying out a warning generation procedure adopted in a conventionalsecurity system;

FIG. 2 is a view illustrating an exemplary configuration of a securitysystem in accordance with an embodiment of the present invention;

FIG. 3 is a flow chart illustrating a method for generating a warningusing edge detection in accordance with an embodiment of the presentinvention; and

FIG. 4 is a view explaining the warning generation method in accordancewith the embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, preferred embodiments of the present invention will be described indetail with reference to the annexed drawings. In the followingdescription, a detailed description of known functions andconfigurations incorporated herein will be omitted when it may make thesubject matter of the present invention rather unclear.

FIG. 2 is a view illustrating an exemplary configuration of a securitysystem in accordance with an embodiment of the present invention. Indetail, a blind detector 24 is added to a back stage of a video decoder20 included in the conventional security system adopting a DVR (DigitalVideo Recorder).

Referring to FIG. 2, a video camera photographs a surveillance area andprovides a captured video image signal in the form of a composite videosignal. A plurality of video cameras can be conventionally installedaccording to the surveillance area.

One video decoder 20 corresponds to one video camera, and performs A/D(Analog/Digital) conversion and decoding for a composite video signaloutputted from the video camera. The video decoder 20 detects asynchronous signal from the composite video signal, and extracts aluminance signal and a color signal from the composite video signal tooutput the extracted luminance and color signals.

A video processor 22 processes the decoded video image signal outputtedfrom the video decoder 20 so that a divided screen image can bedisplayed on a display. The video processor 22 includes horizontal andvertical scalers, a frame memory and a memory controller, and alsoincludes a moving picture compressor for compressing and storing apredetermined video image in a recorder, and a decompressor.

A blind detector 24 filters a high-frequency component of the luminancesignal separated by the video decoder 20, detects edge components fromvideo image signals, extracts only values of the edge components withina range of a predetermined first threshold value, accumulates theextracted values for one video image, and generates a warning signalwhere the accumulation value is smaller than a predetermined secondthreshold value. The blind detector 24 includes an HPF (High PassFilter) arranged at its front stage to detect the edge components fromthe video image signals.

High-frequency components exist in the video image signals of anobject's interface regions having different luminances. Thus, thepresent invention generates a warning sound based on the detection of ablind screen state by comparing a threshold value with an accumulationvalue of the detected edge components after filtering the extractedluminance signal on the basis of the HPF. The “blind screen state” isdefined as a state when a camera lens is blinded by a cover.

A method for generating a warning in the security system having theabove-described system elements will be described with reference toFIGS. 3 and 4.

FIG. 3 is a flow chart illustrating a method for generating a warningusing edge detection in accordance with an embodiment of the presentinvention; and FIG. 4 is a view explaining the warning generation methodin accordance with the embodiment of the present invention.

Referring to FIG. 3, the present invention detects edge components fromone video image, and determines, on the basis of a result of thedetection, whether the warning should be generated. That is, if onevideo image is inputted, the blind detector 24 initializes anaccumulation value (H-sum) to “0” at step 30. A high-frequency componentof a luminance signal, inputted by the HPF arranged at a front stage ofthe blind detector 24, is filtered, and the edge components are detectedfrom the video image. To extract a contour of an object from the videoimage, the present invention employs the HPF (e.g.,H(z)=−0.5z˜+1˜−0.5z{circumflex over ( )}−1) for use in emphasizing acontour of a video image signal. The HPF can employ two filters todetect edge components in horizontal and vertical directions. In thiscase, an adder for adding outputs of the two filters is added. Tosimplify a configuration of hardware, an HPF for detecting only edgecomponents of the horizontal direction can be employed.

As described above, if the HPF detects samples (f_sample) of the edgecomponents, absolute values of the samples are obtained at step 32. Alower threshold value (threshold_Low) is subtracted from an absolutevalue of a sample, and a new sample value as a predetermined firstthreshold value is obtained at step 34. The reason why the lowerthreshold value is subtracted from the absolute value is to eliminatecomponents of interface regions of an object, noise, etc., that are notactually viewable. If the new sample value is smaller than “0”, the newsample value is set as “0” at step 36. If the new sample value(F_sample) obtained at the above step 34 is greater than a predeterminedupper threshold value (threshold_High), the new sample value is set asthe upper threshold value at step 38. The reason why the now samplevalue is set as the upper threshold value is to prevent a malfunctiondue to white noise contained in a video image having a contour componentof a relative larger value, so that it cannot be not selected as anappropriate video image even though only part of the image has a clearcontour component. FIGS. 4(a), 4(b) and 4(c) are views explainingpost-processing of the edge components detected through the HPF.

The present invention extracts only values within a range of apredetermined first threshold value from the edge components detectedthrough the HPF, and an accumulation value (H_sum=H_sum+f_sample) forone video image is obtained from the extracted values at step 40. If allthe edge components for one video image have been accumulated at thestep 42, the blind detector 24 determines, at step 44, whether anaccumulation value (H_sum) of the edge components for the one videoimage is smaller than a predetermined second threshold value(threshold_total). The second threshold value (threshold_total) can bevariably set according to a screen video image captured by a videocamera. As a result of the determination at the above step 44, if theaccumulation value of the edge components for one video image is smallerthan the predetermined second threshold value, the blind detector 24outputs a warning signal to a warning generator in order to enable thewarning generator to generate a predetermined warning sound at step 46.

Thus, the surveillant receives the warning sound and can perform a rapidaction in response to an emergency situation.

Industrial Applicability

As apparent from the above description, the present invention canmaximize efficiency of a security system by determining an inappropriatesignal input to generate a warning sound, even though an intruder blindsa camera lens using a cover.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope of the invention.Accordingly, the present invention is not limited to the above-describedembodiments, but the present invention is defined by the claims whichfollow, along with their full scope of equivalents.

1. A method for generating a warning using edge detection in a securitysystem for receiving video image signals outputted from a plurality ofvideo cameras, and displaying or recording the video image signals,comprising the steps of: a) decoding video image signals and extractingluminance signals from the decoded video image signals; b) filteringhigh-frequency components of the extracted luminance signals anddetecting edge components within the video image signals; c) extractingonly values within a range of a predetermined first threshold value fromthe detected edge components; d) accumulating the detected edgecomponents for one video image; and e) operating a warning device if anaccumulation value is smaller than a predetermined second thresholdvalue.
 2. The method as set forth in claim 1, wherein the range of thefirst threshold value includes an upper threshold value and a lowerthreshold value for use in removing white noise and a luminancecomponent, which cannot be identified.
 3. The method as set forth inclaim 1, wherein the second threshold value is variably set according toa screen video image captured by a video camera.
 4. A security system,comprising: a plurality of video cameras for providing video imagesignals captured from surveillance areas; a plurality of video decoderfor decoding video image signals from the video cameras and extractingluminance signals from the video image signals; and a blind detector forfiltering a high-frequency component of the luminance signal extractedfrom a corresponding video decoder, detecting edge components from thevideo image signals, extracting only values within a range of apredetermined first threshold value, accumulating the extracted valuesfor one video image, and generating a warning signal if an accumulationvalue is smaller than a predetermined second threshold value.
 5. Thesecurity system as set forth in claim 4, wherein the second thresholdvalue is variably set according to a screen video image captured by avideo camera.